Outline
• Disinfection Basics
▫ Why
▫ Types
• Ultraviolet Disinfection Technologies
• Case History – Charlotte, MI
▫ Existing Cl2 Chambers
▫ Hydraulic Issues
▫ Selected Technology
▫ Project Design
▫ Construction Progress
Wastewater Disinfection
• Critical component of wastewater treatment
• Wastewater contains dozens of potential pathogenic viruses, bacteria, and protozoa.
▫ Crypto, E-coli, Giardia
Images: CDC.gov
Diseases that can be passed through
non-disinfected wastewater
• Dysentery
• Typhoid Fever
• Cholera
• Gastroenteritis
• Giardiasis
• Hepatitis A
• Cryptosporidiosis
• Salmonellosis
• Etc…….
Types of Disinfection
• Chlorination
• Ultraviolet
• Ozone
• Chlorine Dioxide
• Chloramination
• Peracetic acid
• Pasteurization
Chlorination
• Disinfection Basics
▫ Direct oxidation/destruction of the cell wall
(lysis)
• Types:
▫ Chlorine Gas
▫ Sodium Hypochlorite
Liquid
Tabular System
On-site Generation
Chlorination
• Advantages:
▫ Reliable, easy to operate, familiar, and cost effective
• Disadvantages:
▫ Chlorine gas is toxic, safety risk
▫ Corrosive
▫ Residual can be harmful to aquatic systems
▫ Toxic Disinfection Byproducts (trihalomethanes)
(ex; chloroform)
Chlorination
• Removing Residual
▫ Sulfur dioxide
▫ Sulfite Salts
Sodium sulfite
Sodium bisulfite
Sodium metabisulfite
▫ Polishing Pond
Ozone
• Disinfection Basics
▫ Cell lysis through oxidation
▫ Produces powerful oxidant hydroxyl radicals
• Application:
▫ Via Contact Chamber
▫ On-site generation
Ozone
• Advantages
▫ No toxic disinfection byproducts
▫ No residual removal
▫ Also reduces odor
▫ Short contact time
• Disadvantages
▫ Ozone in high levels is toxic to humans
▫ Off gas from contactors must be destroyed
Chlorine Dioxide
• Disinfection Basics
▫ Direct Oxidation/Cell Lysis
• Advantages
▫ Highly effective
▫ Minimized disinfection byproducts
• Disadvantages
▫ More expensive than chlorine
Chloramination
• Formed from reaction of ammonia and chlorine.
• Disinfection Basics:
▫ Cell lysis through oxidation
• Advantages:
▫ Ammonia ties up chlorine preventing organochloramines (non-germicidal)
▫ Minimize THM and other disinfection byproducts
• Disadvantages:
▫ Difficult to control due to potential for variable ammonia in wastewater
Peracetic Acid
• Mixture of acetic acid and hydrogen peroxide
• Colorless with Strong Odor
• Newer technology – first in US was 2005
• Disinfection Basics
▫ Cell lysis through oxidation
Peracetic Acid
• Advantages:
▫ no toxic byproducts
▫ short contact time
▫ ease of implementation
▫ low capital
▫ no subsequent process (dechlorination)
• Disadvantages:
▫ increased organic content in effluent
▫ high operational cost due to availability
Pasteurization • Disinfection Basics:
▫ Thermal inactivation
▫ Rapidly heat wastewater effluent to min 180 degF for minimum time 10 mins
Pasteurization
• Disinfection Basics: ▫ Thermal inactivation ▫ Rapidly heat wastewater effluent to min 180
degF for minimum time 10 mins
• Advantages: ▫ no toxic byproducts ▫ short contact time ▫ no subsequent process (dechlorination)
• Disadvantages: ▫ Need heat! ▫ Also need to cool to prevent damage to discharge
Ultraviolet Disinfection
• Disinfection Basics:
▫ Induces photo-biochemical change in microorganisms (renders sterile)
▫ Dimerization of nucleic acids (DNA and RNA) and proteins
▫ Most effective at 254 nM wavelength
Ultraviolet Disinfection
• Advantages:
▫ Safer than using chemicals
▫ No residuals to remove
▫ Short Contact time
▫ Cost Effective
• Disadvantages:
▫ Need relatively “clear” water
▫ Bulb life is ~1.5-2 years
Types of UV Disinfection Lamps
• Low Pressure, High Intensity
• Medium Pressure, High Intensity
• Low Pressure, Low Intensity
Case History – Charlotte, MI
• Plant = .9 MGD Average Flow
• Screening and Grit Removal, Primary Clarifiers, Trickling Filters, Final Clarifiers, Tertiary Filtration, then Cl2 and Bisulfite
• Outfall to Battle Creek
Design Challenges
• Average Flow = .9 MGD, but Design UV system for plant Peak flow = 4.86 MGD
• Low amount of head to work with between inlet to chamber and outlet
• Parshall Flume to measure effluent flow
• Tertiary filters require backwash reservoir
• Limited Space within existing tank
Design Elements
• Magnetic Flow Meter
▫ Gooseneck outlet piping
• Parallel UV Channels
▫ Limited space for series
▫ S-pattern wouldn’t allow for hydraulics
• Inlet gates for flow control and energy savings
▫ Each channel rated for 2.4 MGD
▫ Turn off when flows are low
• Fixed Finger Weirs
Hydraulic Challenges
dv(GPM) Cycle time (min) v(gal)
dvin(0-19) = 347.22 19.00 6597.22
dvout(0-4) = 1500.00 4.00 6000.00 ***1400 GMP + 100 GPM Surface Wash
dvout(5-9) = 1800.00 5.00 9000.00
dvout(10-19)
= 1500.00 10.00 15000.00 ***1400 GMP + 100 GPM Surface Wash
Total Volume In Total Volume Out Volume Needed
6598 30000 23402
Volume Needed Excess Volume Construction Excess Volume Post Construction
23402 2628.47 10173.30
• Tertiary Filter Backwash Volume
O&M Costs– Charlotte, MI
• Chlorine Costs/Year = $3,000
• Bisulfite Costs/Year = $3,500
• System Maintenance Costs/Year $3,000
• Safety Equipment Costs/Year $1,000
TOTAL EXISTING O&M/yr $10,500
• Energy and Maintenance on UV/Yr = $5,000
Questions?
Brian Hannon, P.E. Moore & Bruggink, Inc. [email protected] (616)363-9801
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